Role of GeneXpert in the diagnosis of mycobacterium tuberculosis.

Introduction: GeneXpert (GX) is a novel, integrated, cartridge-based, nucleic acid amplification test with an established role for rapid diagnosis of Mycobacterium tuberculosis and detection of rifampicin resistance.

Aim: To evaluate the role of GX in pulmonary and extrapulmonary tuberculosis (TB) cases.

Material And Methods: A prospective study was conducted in the pulmonary medicine department of a tertiary care hospital after the Ethics Comittee permission. Data of 257 presumptive TB patients was retrieved for GX, acid fast bacilli smear and cul-ture (AFB smear and culture) and drug susceptibility test (DST). Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) of GX in diagnosis and determination of rifampicin resistance in pulmonary and extrapulmonary TB cases were calculated and compared with culture and DST results.

Results: Our study included 132 pulmonary and 125 extrapulmonary cases. On the basis of clinicoradiological and microbiological correlation, diagnosis of TB was confirmed in 104 pulmonary and 103 extrapulmonary cases. Out of a total of 104 pulmonary TB cases, 73 were rifampicin-sensitive and 31 were rifampicin-resistant cases. 103 extrapulmonary TB patients included 66 rifampicin-sensitive and 37 rifampicin-resistant cases. The sensitivity, specificity, PPV, NPV of GX in diagnosis and detection of rifampicin resistance in pulmonary TB was 95%, 93%, 98%, 84% and 96%, 100%, 100%, 96%, respectively. The sensitivity, specificity, PPV, NPV of GX in diagnosis and detection of rifampicin resistance in extrapulmonary TB cases was 79%, 86%, 96%, 47% and 97%, 95%, 97%, 95%, respectively.

Conclusions: GX results are superior to smear microscopy and comparable to culture with shorter turnaround time.We recom-mend using it in routine TB diagnosis as this will expedite the management of patients with presumptive TB.